Mobile communication systems include systems in which one modulation scheme is selected from a plurality of modulation schemes when signals are modulated. Systems which are devised so that this selection is performed automatically are called adaptive modulation schemes. In mobile communication systems using adaptive modulation schemes, each communication apparatus determines the modulation scheme of the signal to be transmitted next by this communication apparatus on the basis of the received power, which is one piece of receiving environment information indicating the receiving environment of signals received from the communication counterpart (for example, see Patent Document 1). The reason for this is that the received power required in order to receive signals (necessary received power) differs according to the modulation scheme.
Ordinarily, this adaptive modulation is performed in each time slot. Each time slot includes a header portion which contains a control bit sequence, and a payload portion which contains the communication content, in the stated order. An adaptive modulation scheme is performed so that the header portion is transmitted and received by a predetermined modulation scheme, and information indicating the modulation scheme of this time slot is contained in the control bit sequence contained in the header portion. The receiver demodulates the payload portion of this time slot using the modulation scheme indicated by this information.
[Patent Document 1] Japanese Laid-Open Patent Application No. 2004-297127